The inner surface of a pneumatic tire is typically comprised of an elastomeric composition designed to prevent or retard the permeation of air and moisture into the carcass from the tire's inner air chamber. It is often referred to as an innerliner. Innerliners have also been used for many years in tubeless pneumatic vehicle tires to retard or prevent the escape of air used to inflate the tire, thereby maintaining tire pressure. Rubbers, such as butyl and halobutyl rubber, which are relatively impermeable to air are often used as a major proportion of the innerliners.
The innerliner is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and their methods of preparation are well known to those having skill in such art.
Halobutyl rubber is generally the most expensive rubber used in a tire. Given the competitive tire market and the continued need to lower the cost of manufacturing tires without sacrificing properties, there exists a need to eliminate or substantially decrease the cost of innerliners which perform such an important function in the performance of a tire.
Acrylonitrile/butadiene copolymers are commonly known for having excellent air impermeability. Since acrylonitrile/butadiene copolymers are conventionally more economical than halobutyl rubbers, one would hope that such acrylonitrile/butadiene copolymers could be utilized as an innerliner. Unfortunately, acrylonitrile/butadiene copolymers suffer from unacceptable flexural properties at low temperatures. Since a rubber used in an innerliner must be flexible and the service life of a pneumatic tire commonly involves severe low temperatures, the use of an acrylonitrile/butadiene copolymer as an innerliner would be expected to meet with failure.